The long-range goal of this project is to develop a novel and effective strategy for allograft tolerance induction. To accomplish this goal, we will create an "engineered veto cell" and apply it in a preclinical non-human primate model of kidney transplant to induce durable tolerance with non immunosuppressive treatment beyond the peritransplant tolerance induction period. This study is unique in that it uses novel gene transfer technology to exploit the veto effect to kill or inactivate recipient alloreactive cells. Our approach to tolerance induction combines genetic modification of donor dendritic cells (DC) with brief immunosuppressive treatment, a combination that builds upon our previous studies of tolerance induction with donor bone marrow in the rhesus model. The research plan will develop and utilize customized gene transfer methods to constitutively express TGF-beta1 in donor dendritic cells (dDC) in order to deliver within the microenvironment of T cell-dDC cross talk, a lethal signal to the responding donor-specific T cells. We propose that when used in conjunction with a short treatment with anti-thymocyte globulin, TGF-beta1 engineered dDC will effectively function as "ersatz veto cells" to induce clonal deletion and specific tolerance. A requisite condition for achieving our goals is the genetic modification of dDC with high efficacy and in a manner that does not impact unfavorably in their functionality as antigen presenting cells (APC). A variety of vector approaches have been explored to achieve effective transduction of DC to express heterologous genes relevant to this strategy and others. Available gene transfer methods, however, have represented a major limitation, as current generation vectors are generally of low efficiency and/or may be associated with significant toxicity for DC. For successful transplantation to clinical practice in transplantation and also for other immunological applications (e.g., autoimmune disease, cancer, and vaccines), there is a need to develop improved vector systems for genetically modifying DC. In this regard, we have developed methods to alter the tropism of adenoviral (Ad) vectors as a means to enhance their efficacy profile. We have demonstrated that an immunologic re-target approach allows re-routing of Ad vectors via the CD40 pathway of human DC with dramatic enhancements of efficiency and with beneficial effects in immune presentation function. In the proposed studies, the Ad TGF-beta1 DC cellular construct will be first optimized for in vitro reduction of allospecific cytotoxic T cell (CTL) responses in the monkey model. The final goal is proof of principal for the employment of TGF-beta1 dDC in a preclinical setting using the well-established kidney transplant model in rhesus macaques. Although we expect that these studies will yield novel approaches for induction of tolerance in the context of kidney transplantation, our general strategy might also be extended to the transplantation of other organs and tissues. In addition, the propose tolerance strategy will also be applicable to those recipients, who by virtue of high diphtheria sensitization or other causes, are not candidates for treatment with the potent diphtheria based anti-CD3 immunotoxin described in Projects 1 and 2. Finally, vector developments and analyses proposed herein may allow the use of tropism-modifier adenovirus as a gene delivery method for genetic modification of DC, and will elucidate key aspects of the immune response generated in vivo against Ad vectors.